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TDI Conversions Discussions on converting non TDIs into TDIS. More general items can be answered better in other sections. This is ideal for issues that don't have an overlap and are very special to swaping engines.

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Old September 7th, 2017, 12:05   #1
archemitis
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Default ALH coolant flow question

Sorry to ask such a seemingly easy question to answer, but... Which way does the coolant flow on an ALH? Thermostat routed to the lower radiator hose or upper? Thanks in advance. Every diagram I clicked on was a bad link.
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Old September 7th, 2017, 13:50   #2
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Tstat is on the lower hose. Coolant flows in there and out through the head to the top radiator hose...Hope this helps
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Old September 8th, 2017, 16:16   #3
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Thanks so much! I was pretty sure untill I saw a few conversions done backwards!
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Old September 10th, 2017, 05:16   #4
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Thanks so much! I was pretty sure untill I saw a few conversions done backwards!
yeah, and those guys will find out soon enough that when the coolant gets just a little bit low the water pump stops pumping
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Old September 10th, 2017, 08:47   #5
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It is still odd the way VW plumbed it
Normally the tstat is on the hot hose on top(relatively speaking)of the engine
Took me awhile to get my head around this, as there is a passage in the block where the coolant(hot) passes over the tstat
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Old September 10th, 2017, 20:30   #6
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Quote:
Originally Posted by Lone Ranger View Post
It is still odd the way VW plumbed it
Normally the tstat is on the hot hose on top(relatively speaking)of the engine
Took me awhile to get my head around this, as there is a passage in the block where the coolant(hot) passes over the tstat
Having the thermostat at the lower hose is quite common in all modern-ish engines from all manufacturers. When the thermostat opens in this arrangement, the relatively low temperature coolant from low part of the radiator comes into contact with it immediately, causing it to shut sooner or at least not open as far as it otherwise would if it were at the upper hose. The effect is less drastic swings in engine temperature during operation. Emissions
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Old September 14th, 2017, 08:24   #7
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emissions, and far more stable operating temperatures. That gives you more consistent performance and makes it easier to tune
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Old September 16th, 2017, 16:08   #8
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Yep, I wasnt knocking it. It performs flawlessly.
Just for a small block ford guy this arrangment is kinda backwards

In winter with no coolant glow plugs and egr put to the lowest possible it struggles to stay in the 80s. As soon as it idles its 55-60 in about 3 minutes. I've thought about a temp jerry rig to move it to the top hoses and would if I knew it would make it a little warmer haha
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Old September 20th, 2017, 09:33   #9
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Get yourself a 92C thermostat and call it a day.. Napa part number ATM-143992K2 for a Calorstat brand, or ATM-TX1392D for Behr brand.

I have the Calorstat one in mine and it will run 197-204F on my Torque app on the highway even when it's -15F outside..
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Old September 20th, 2017, 09:41   #10
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Quote:
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Yep, I wasnt knocking it. It performs flawlessly.
Just for a small block ford guy this arrangment is kinda backwards

In winter with no coolant glow plugs and egr put to the lowest possible it struggles to stay in the 80s. As soon as it idles its 55-60 in about 3 minutes. I've thought about a temp jerry rig to move it to the top hoses and would if I knew it would make it a little warmer haha
Veeeery common for these thermostats to stick partly open or start opening early as they age... The location is fine, you may have a weak t-stat.

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Old September 27th, 2017, 09:24   #11
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The return coolant from the Oil Cooler, Expansion Tank, EGR Cooler, and Heater Loop all end up at the Water Pump housing where the T-stat is located. That source of "hot" coolant is what causes the T-stat to open and allow flow from the radiator bottom hose. That design or very similar, goes all the way back to the 1974 VW Rabbit engines.
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Old September 27th, 2017, 16:56   #12
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The return coolant from the Oil Cooler, Expansion Tank, EGR Cooler, and Heater Loop all end up at the Water Pump housing where the T-stat is located. That source of "hot" coolant is what causes the T-stat to open and allow flow from the radiator bottom hose. That design or very similar, goes all the way back to the 1974 VW Rabbit engines.
good point
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Old September 27th, 2017, 17:12   #13
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What happens when there is no thermostat installed.
I just found that my AHU did not have one
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Old September 27th, 2017, 18:06   #14
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Diesel Sammy, with no T-stat, the engine could actually run hot as the coolant would flow through the Rad too fast (especially in summer). During the winter months, the Engine would not warm up to normal operating temp.
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Old September 27th, 2017, 18:16   #15
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FWIW, I've seen Threads/Posts about "trapped" air in engines, especially Subie engines in the Vanagons. My experience, the VW engine coolant system purges air extremely well. I've never had an issue purging air out of the coolant system in the ALH in my Vanagon ................ long rad hoses and heater hoses all the way to the front (engine in rear)...... never an issue!

The Water Pump is extremely efficient moving the coolant. I have the expansion tank tapped for a fitting, tube, etc., to a pressure gauge up front in my Vanagon. The gauge registers from 0-15 PSI. The coolant system very seldom goes above 7 to 9 psi. ........... As for efficiency, when I rev the engine or as I go through the gears, RPMs climbing, I can see the pressure drop because the water pump is pulling coolant out of the expansion tank (as well as the other returns)... very interesting !
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